1. Field of the Invention
The present invention generally relates to a multi-induction loop layout of an electromagnetic inductive system, and more particularly to a method for locating the coordinates of the multi-induction loop layout of an electromagnetic inductive system.
2. Description of the Prior Art
Since a handwriting input device can replace a mouse and allow users to input words and pictures by hand, more easily than a mouse, the field of improvement of a handwriting input device has developed rapidly in recent years. The early handwriting input device replaces a mouse with a pen. In order to increase the convenience of operation for the user, a cordless pointer device, such as a pen, a mouse, a puck or a stylus with a digitizer tablet is usually used. The tip of the cordless pen or stylus corresponds with the left key of the mouse. Although conventional pen-input products have existed for several years, similar kinds of products generally focus on the application of a single function such as graphing, drawing or Chinese text key-in.
The conventional electromagnetic inductive system is equipped with a digitizer tablet and a mouse or pen-transducer/pointer device. Generally speaking, there are two modes of presented the position the pointer device located on the active area of the tablet: the relative mode and the absolute mode. The mechanical or optical type mouse device generally functions in the relative mode, that is to say, when the mouse glides on the surface of the mouse pad, the computer system receives the cursor information from the mouse and it can only identify the relative movement in X and Y directions. A common technique is to implement a pair of mutually perpendicular altering signals in the mouse, these two signals corresponding to the longitudinal and transverse movement of the mouse. In contrast, the cursor device of the tablet, such as cordless pointer device, generally functions in the absolute mode. As far as the computer system is concerned, once the pointer device is operated and moved to another place on the active area of the tablet, the signal changes in order to response the new absolute coordinates of the pointer device. Nowadays, there have already been several methods for positioning the pointer device on the active area of the tablet, and the electromagnetic field inductive technique is the technique that generally applies to the absolute mode. The early transducer/pointer devices were connected to the tablet with a set of wires, delivering the information of coordinates and switch/pressure status to the computer system with interface. Some cordless transducers/pointer devices in the prior art indicated the use of different functions by changing the frequency and/or phase, the functions included, pressing down the button, pressing the tip of the pointer device on the active area, and other similar functions. However, without careful handling, the change in frequency and phase could easily cause misjudgment in the desired function of the pointer device because of various external factors such as metallic objects, noise signals, exterior electromagnetic fields, etc. These problems become extraordinarily obvious when it comes to tablets of larger size. The conventional technique for improvement made to the tablet system, allows users to operate the pointer device with tablet system in dual mode, and therefore the information regarding relative mode and absolute mode can both be provided under the user's control.
The current pointer/input product is usually an electromagnetic inductive system. The electromagnetic inductive system usually comprises an electromagnetic pointer device and a tablet. The electromagnetic pointer device has an oscillation circuit and a battery, providing energy for transmitting the relative electromagnetic signal. Take the electromagnetic pointer device for example, when the tip of the pointer device is pressed, the inductance of the inductor changes, therefore the oscillation frequency also changes. The higher the pressure received by the pointer device, the greater the inductance changes, and the oscillation frequency, therefore the amount of the pressure exerted upon the pointer device tip of the can be obtained through the changing degree of frequency. There are also two switch keys on the side of the pen type cordless pointer device, the on/off status changes the transmitting frequency and the connecting/disconnecting a specific capacitor in the oscillation circuits. When the user presses the switch key, it can be identified through detecting the variation of frequency. The tablet also comprises elements such as a detective loop, an amplifier, and an ADC and so on. The central writing area of this conventional handwriting tablet is plaited by inductive loops, the layout is composed of double layers of a PCB and the inductive loops with two axial arranged in an array of equal distance. The major use of these inductive loops is to induce the electromagnetic signal transmitted by the electromagnetic pointer device. When the electromagnetic pointer device transmits the electromagnetic signal, these inductive loops will induce the electromagnetic signal and the microprocessor will receive the processed information of the pointer device through a signal processing circuit.
Generally speaking, the inductive loops of the conventional electromagnetic inductive device and its layout design makes the inductive loops a grid net with the X and Y axis arranged in an array at equal distance in order to induce the signal emitted from the electromagnetic pointer device and figure out its absolute coordinates. Referring to the inductive loops layout deployed according to the X direction of a two-dimensional orthogonal coordinate indicated in FIG. 1A. One terminal of each antenna loop 110A is connected respectively with one switch (from X1 to X25). The other terminal is connected with the common ground node 105A, through which, the signal induced by each antenna loop 110A can be obtained by controlling the switches X1 to X25 in order. Since the intensity of the magnetic field is an inverse proportion to the square of distance, the farther the distance between the electromagnetic pointer device that's transmitting the electromagnetic field and the inductive loops, the weaker is the signal induced by the inductive loops; in contrast, the nearer the distance between the electromagnetic pointer device that's transmitting the electromagnetic field and the inductive loops, the stronger is the signal induced by the inductive loops. Therefore, as long as the microprocessor of the tablet can scan through all the inductive loops one by one in sequence, and analyze the strength of the signals induced by each inductive loop, the inductive loops in which dominates the range the electromagnetic pointer device located can be identified. The coordinates of its position can be figured out. However, as far as a tablet of a larger size is concerned, the number of inductive loops arranged also increases, and therefore more loop switches are needed.
On the other hand, the development of current information products is aimed at a high-speed and high data rate process with multiple and excellent functions. But as the speed of processing and data rate increase, the phenomenon of electromagnetic interference will happened often. In some specific occasions of operating tablet system, there are usually other information products being used. Therefore the conventional tablet is easily interfered with by exterior electromagnetic fields and thus misjudgment is a result. As far as the tablet of a larger active area is demanded in commerce is concerned, the number of inductive loops needed increases, and therefore the number of loop switches will also increase greatly without a doubt. Referring to the conventional inductive loops layout in FIG. 1B, the inductive loops of X axis and Y axis are connected respectively with the common ground node 105A and 105B. The deployment of the inductive loops 110A and 110B will exceed the region of the common ground node 105A and 105B in order to form a close-like region. Therefore, the conventional tablet must reserve space bounded 170 to place the initial terminal of the inductive loops 110A and 10B that exceeds the common ground node 105A and 105B. This limits the miniaturization of a PCB for a handwriting tablet and makes it difficult to design and produce a tablet with the small boundary. In view of this, the present invention provides a multi-induction loop layout of the electromagnetic inductive system to eliminate the defect mentioned above.